1. Field of the Invention
This invention relates to document reproduction, such as by xerographic copiers or printers and, more particularly to such equipment having enhanced capabilities for copying or scanning nonplanar originals, such as bound books and three dimensional objects.
2. Description of the Related Art
In reproduction machines, the copying of non-planar originals, such as bound books, presents a problem because it is difficult to copy the information adjacent the binding of the book. The difficulties of reproduction in the binding area results from the portion of the book adjacent the binding being lifted away from the original image plane, which is usually defined by a planar transparent plate. The quality of the reproduction decreases in relation to increasing distance of the original image from the image plane. The lack of clarity and/or distortion in the copy results from several factors including 1) the projected image becomes increasingly out of focus as the original is scanned in the central binding area; 2) the illumination becomes less than optimal in the spine area; 3) there is compression of the image data along the scan length; and 4) there is degradation of the definition of the image data resulting from the original image being disposed at an angle to the image plane.
Various approaches have been taken to minimize or eliminate these factors. A common "brute force" approach is to press the book against the surface of the platen to lessen or eliminate displacement from the platen surface of the binding. However, portions of the pages adjacent the binding area still remain a short distance above the platen surface. Consequently, information contained in these portions is out of focus on the output sheet. Moreover, attempts to press the binding area closer to the platen can result in breaking the binding of the book, especially older books, which have brittle bindings.
Another solution is to modify the platen to have a sloping edge portion so that the bound part of the book is placed in a corner position so that the entire surface of the page being copied is in intimate contact with the platen surface. An example of such a system is disclosed in U.S. Pat. No. 3,775,008. These systems have several disadvantages. The magnification range is limited because of restriction on scanner movement in the sloping corner edge. Also, copying capabilities are limited by the inability to employ a "split scan" scanning system, which allows both pages of a book to be placed on a platen and scanned without repositioning.
Another development is a system employing a height sensor on the scanner for determining the height of the original image above the platen. The height information is used to control the position of a scanning mirror to adjust visual image position, to adjust variable focusing, to control scan speed, and to control illumination. Such a system is disclosed in U.S. patent application Ser. No. 07/526,743 filed May 22, 1990, entitled DOCUMENT REPRODUCTION MACHINE WITH ENHANCED BOOK COPYING CAPABILITY and owned by the Assignee of the present application, the disclosure of which is herein incorporated by reference. Although the above mentioned system overcomes many of the shortcomings mentioned above, it requires the need for precise positioning of mirrors and precise controllability of focusing lenses and carriage speeds. These factors add to the complexity of the equipment and increase its cost.